The Applicant has developed a range of Memjet® inkjet printers as described in, for example, WO2011/143700, WO2011/143699 and WO2009/089567, the contents of which are herein incorporated by reference. Memjet® printers employ a stationary printhead in combination with a feed mechanism which feeds print media past the printhead in a single pass. Memjet® printers therefore provide much higher printing speeds than conventional scanning inkjet printers.
High-speed single-pass inkjet printing requires accurate media handling, especially in the print zone of the printhead, in order to provide acceptable print quality. For relatively narrow print zones (e.g. A4 size or narrower), a system of entry and exit rollers in combination with a fixed media platen generally provides sufficient stability in the print zone (see, for example, U.S. Pat. No. 8,523,316, the contents of which are herein incorporated by reference). However, for wider media widths and/or faster print speeds, more complex media feed mechanisms are required to provide acceptable print quality. For example, U.S. Pat. No. 8,540,361 describes a feed mechanism suitable for wideformat printing comprising a combination of a fixed vacuum platen, an upstream drive roller and a downstream vacuum belt mechanism.
Vacuum belt mechanisms are an attractive means for moving print media at high speeds through a print zone. Various vacuum belt mechanisms for high-speed printing are described in, for example, US 2007/0247505, US 2007/0035605, US 2008/0218576, U.S. Pat. No. 6,328,439, U.S. Pat. No. 6,698,878 and WO02/78958. Referring to FIGS. 1A and 1B, prior art vacuum belt mechanisms typically comprise an endless belt 1 tensioned between a first roller 3 positioned upstream of a print zone 5 and a second roller 7 positioned downstream of the print zone. A printhead assembly 9 is positioned over an upper surface of the belt 1 while a vacuum blower 11 is positioned below the belt for suctioning print media onto the upper surface. The printhead assembly 9 is liftable away from the belt to allow intervention from a maintenance station 13, when required (FIG. 2A). Likewise, the entire vacuum belt mechanism 10 may be movable away from printhead assembly 9 to facilitate clearance of paper jams.
A problem with prior art vacuum belt mechanisms, such as the mechanism described in connection with FIG. 1A, is that the belt may become fouled with ink. Ink mist generated in the print zone during printing is drawn towards the belt by the vacuum blower, thereby fouling the belt and, consequently, fouling paper in contact with the belt. Furthermore, it is desirable for inkjet printheads to spit ink regularly so as to avoid nozzles becoming clogged with a plug of viscous ink. Typically, inkjet printheads perform a number of inter-page spits so as to reduce the frequency of maintenance interventions. However, endless belts are not amenable to inter-page spitting due to ink fouling.
It would be desirable to provide a printer having a belt assembly suitable for high-speed inkjet printing.